Spark plug electrode



Sept. 14, 1948. 1-. a. McooueAL 2,449,403

SPARK PLUG ELECTRODE Filed April 2-. 1945 W m 7. w M, w n a ll 3 m h m 0 M H z a a m I r F. 0 Z K z i l, I 1 1 ux/AZ Z2Z72277277222272 4 I i #m w w Q I y x W A g Ill x \w\\ H\\ x fl M V g e, z

Patented Sept. 14, 1948 I SPARK PLUG ELECTRODE Taine G. McDougal, Flint, Mich., assignor to General Motors (nrporatiom Detroit, Mich, a corporation of l. laware Application pril 2, 1945, Serial No. 586,132

6 Claims.

The present invention relates generally to spark plugs and more particularly to certain improvements in the construction of the center electrode and its mountting in a plug adapted primarily for aircraft engines.

With increases in power output of-aircraft engines and the use of higher grades of fuels the increased pressures and temperatures in the combustion chamber to which the spark plug is subjected require special precautions to prevent carbon fouling, preignition, and rapid wear of the sparking points of the plug.

To improve spark plug operation and life under such engine conditions as have been encountered in recent years, it has been proposed, among other developments, to control the temperature of the center electrode as disclosed, for example, in Heller Patent No. 2,296,033 by providing the electrode with a core of relatively high thermal conductivity, and the present invention relates to further improvements of this nature.

According to the present invention, both the inner bore of a tubularacenter electrode and a space between the outer wall of this electrode and the insulator in which it is mounted are filled with silver or some material having suitable heat conductivity which is cast in place in the manner to be described herein.

In the drawing:

Figure 1 is a vertical section through a spark plug embodying the present invention.

Figure 2 is an enlarged fragmentary elevation,

assembly.

Referring now to the drawing, an aircraft spark plug has been shown -as consisting of the outer metallic shell I0, metal shielding barrel l2, and shielding barrel insulator l4 having upper and lower cushioning rings I 6 and retainers ii. The core insulator 20 is mounted within the shell i and held in sealing engagement with the internal shoulder 22 of the shell with an interposed gasket 24 by the lower end of the barrel I! which engages a thrust spacer 26 contacting a resilient C-shaped spring 28 to apply downward pressure on the insulator 20 through the washer 30.

The lower end of the shell l0 constitutes the ground electrode and may be formed or provided in the usual manner with spaced prongs 32 for cooperation with the center electrode indicated generally at 34 which is mounted in the insulator 20. The insulator 20 of a suitable ceramic material such as a sintered oxide or porcelain is formed with a longitudinal bore having a lower portion 36 and an upper portion 38 of partly in section, of the center electrode prior to slightly larger diameter to provide an internal ledge adapted to support and position the center electrode.

The electrode 24 which is preferably made of suitable heat and corrosion-resistant material such as nickel or nickel alloy is initially formed with an inner bore to provide a" closed tip 42 and a shank portion 44 having an enlarged shoulder 46 at its upper end to contact the ledge 40 in the insulator 20 with the electrode extending downwardly therefrom through the insulator bore portion 36 and protruding below the insulator to position the tip 42 adjacent the prongs 32 on the shell iii. The outside diameter of the shank portion 44 is reduced between the shoulder 48 and the protruding end thereof to provide an annular space between the electrode and the wall of the insulator bore portion 36, and the wan of the shank portion is transversely drilled adjacent the shoulder 46. to provide openings 48 through thewall. Adjacent the protruding end of the electrode, the wall of the reduced portion is formed with an annular knurl 50 which slightly larger diameter than the protruding portion for a purpose to be hereinafter described.

According to the present invention the inner bore of the electrode and the annular space between the electrode and insulator bore is adapted to be filled with silver or some similar material having relatively high heat conductivity which is preferably cast molten in place in the following manner. the insulator with the shoulder 46 resting on the ledge 40, the silver in the formof a wire or rod of smaller diameter than the bore of the electrode may be inserted in the bore. The amount oi. silver is such that the upper end of the wire or rod will protrude above the electrode and if desired, a current conducting wire coil 52 of nickel or the like may be placed around the upper end of the silver wire or rod in contact with the upper face of the electrode shoulder 46.

The insulator 20 with the electrode 34, silver wire or rod and wire coil 52 in position therein is then placed in a furnace to raise the temperature somewhat above the melting point of the silver. When the silver has become molten, this assembly is centrifuged with the electrode tip extending horizontally outward so that the molten silver, as shown at 54, fills the inner bore of the electrode and also passes through the openings 4! to fill the annular space between the electrode and the bore portion 36 of the insulator. It will also be seen that the lower turns of the conducting wire coil 52 will be imbedded in the cast silver.

is of- After placing the electrode in During the above operation the annular knurl ll which is of larger diameter than the protruding electrode portion tends to inhibit the molten silver from being centrifuged into and out through the relatively smaller clearance which is present between this portion of the electrode below the knurl and the bore 38 oi the insulator 20. Although a very small amount of silver may be forced out through this clearance the provi-- sion of the annular knurl prevents the loss of any appreciable quantity of silver.

The remaining parts oi the insulator assembly such as are located within the insulator bore portion 88 are shown as preferably consisting of a lower seal 58, resistance 58, upper seals 80 and I2, and the core pin 84 with the core contact cap 88. The respective seals may consist of mixtures of glass and conducting material'such as copper and the resistance consists of a mixture of glass and carbon black and these materials introduced into the insulator bore in powdered or pellet form and fused therein as is described in McDougal et al. application Serial No. 488,114, filed May 24, 1943.

With the present construction and mounting of the center electrode the silver which is cast between the electrode and insulator bore and within the hollow electrode provides good heat conductivity or heat dissipation from those portions exposed to the combustion gases and affords a heat conducting path of low resistance from the spark gap at the lower end of the plug upwardly there- -irorn to prevent the electrode tip from exceeding that operating temperature which has been found to substantially eliminate carbon fouling, Dreignition. and rapid wear of the sparking points.

Although the center electrode has been described herein as preferably of nickel or a nickel alloy it will be understood that it may also be of tungsten, stainless steel or similar heat and corrosion-resistant materials and that instead ofsilver as the heat conducting material, other materials having good heat conductivity, such as copper, may be used.

I claim:

1. In a spark plug, an insulator having a bore therein, a tubular electrode in said bore having an exposed closed electrode end and a shank portion within said bore of smaller diameter than said bore to provide an annular space therebetween, an annular knurl on said shank portion adjacent the lower end of said bore to substantially close one end of said annular space, and a material selected for its suitable heat conductivity within said electrode and within said annular space.

2. In a spark plug, an insulator having a'bore and an internal ledge in said bore, a tubular electrode in said bore having an exposed closed lower end and an open upper end within said bore, a shoulder on said electrode adapted to engage the ledge in said bore and a shank portion of smaller diameter than said bore between said shoulder and said exposed lower end of said electrode to provide an annular space between said electrode and bore, an opening through the wall of said electrode adjacent said shoulder, and a material of relatively high heat conductivity cast within said electrode and extending through said opening and filling said annular space between the electrode and the bore in the insulator.

3. In a spark plug, an insulator having a bore erein. a tubular electrode in said bore having an exposed closed electrode end and a shank portion spaced from said bore, said electrode being made of corrosion-resistant metal, and means for conductin heat from said electrode end and securing said electrode within said bore comprising silver which is cast within said electrode and in the space between said shank portion and said 4. In a spark plug, an insulator having a bore therein, a tubular electrode in said bore having an exposed closed lower electrode end and a shank portion spaced from said bore and having an open upper end within said bore, said electrode being made of corrosion-resistant metal, and means for conducting heat from said lower electrode end and securing said electrode within said bore including a material of relatively high heat conductivity which is cast within said electrode and in the space between said shank portion and said bore and which extends within said bore above the upper end of said electrode.

5. A method of making a spark plu having an insulator with a central bore and a tubular electrode having a closed end and an opening through the wall of said electrode, which comprises positioning said electrode in said bore in spaced relation thereto intermediateits ends with the closed end extending beyond one end of said bore, introducing fusible material through the other end of said bore, centrifuging the insulator and electrode with said material in a molten state to cause said material to fill said tubular electrode and the space between said electrode and bore, and letting the material cool therein.

6. A method of making a spark plug having an insulator with a central bore and a tubular electrode having a closed lower end and an opening through the wall of said electrode adjacent the upper open end thereof, which comprises assembling said electrode in said bore in spaced relation thereto intermediate its ends to provide an annular space therebetween and with the closed louver end of said electrode extending beyond one end of said bore, inserting a rod of fusible material into the upper end of said electrode, heating this assembly to render said material molten, centrifuging said assembly with the closed electrode end extending horizontally outward to thereby cause said molten material to fill said electrode and be forced through the'openin in the wall thereof to ill] the annular space between said electrode and bore, and letting the material cool therein.

TAINE G. McDOUGAL.

REFERENCES CITED The following references are of record in the file of this patent:

v STATES PATENTS Number Name Date 1,368,160 Joufiret Feb. 8, 1921 2,081,500 Nowosielski May 25, 1937 2,088,384 Nowosielskl July 27, 1937 2,350,731 Dobrosavljevitch June 6, 1944 

